Larry Floersch
I know summer is just about over, and school has restarted for many of the kids out there, but there is still lots of time to splash in the water before it freezes.
Now, by “splash in the water” I’m not talking Olympic diving here, where the goal is to enter the water while perfectly vertical, keeping your toes pointed, barely making a ripple, and garnering a score of 10.0 from all the judges except the one from North Korea. Nosiree. If you are like the kids I know (and the kid I was long ago), the joy is in making a splash big enough to drench unsuspecting parental figures napping in the sun in lounge chairs on the pool deck and send them screeching and cursing for cover.
But how to create the maximum splash? A ‘cannonball?’ Or maybe a ‘bellyflop?’
Fear not! Scientists are on the task.
As reported in my favorite science news magazine, postdoctoral fellows Pankaj Rohilla and Daehyun Choi at Georgia Tech, who are fluid dynamicists — which I think means they can gracefully consume large quantities of liquids such as beer — became intrigued with the sport of “manu” jumping. Manu is popular with the Māori people of New Zealand, and if you’ve ever seen a bunch of tattooed Māori men the size of Clydesdales perform a traditional haka war dance, you know the Māori take their sports and physical activity very enthusiastically.
The object of manu jumping, which is also known in New Zealand as “bombing,” is to jump from a bridge, dock, or platform and make the biggest splash possible, both in width and height. The Māori have been manu jumping for decades and now even have a world championship competition for the sport.
What Rohilla and Choi found after analyzing 75 videos of manu jumping was that it is all in the technique. Manu jumpers must pull their body into a tight V shape by bringing the knees to the chest and enter the water butt cheeks first. This creates what is called the “crown splash.” Then, in a split second, they force their head down, straighten their body, and open the V. This enlarges the air cavity caused by their body plunging through the water. The water then pinches off the air bubble, and the bubble rises explosively to the surface in what is called a Worthington jet or Worthington splash. The Worthington splash is named after A.M. Worthington, who was the Snowflake Bentley of splashes, using high-speed photography to capture how droplets create splashes as they break the surface of a body of liquid.
Rather than trying to perform manu jumps themselves, no doubt because they were what I as a youth would call “chicken,” the researchers went on to create a little robot that could recreate the movements made by human manu jumpers. They used the “manubot” to measure the optimal angle of entry into the water. Between the robot experiments and analysis of the videos, they determined that angle to be 45 degrees.
If performed perfectly, a manu jump can create a splash over 30 feet high. But if you miss the optimal angle, it can really sting, much like a bellyflop. Even worse, you can be injured.
Such research, of course, does have a purpose beyond fun. Determining how bodies interact with fluids and the physics of water entry are indispensable for fields such as naval engineering and robotics, so knowledge gained from studying manu jumping can have implications in those fields.
But if you’re young and in shape and love making a splash, like the kids I know, consider that this year in a competition in Wellington, New Zealand, the biggest splash earned the manu jumper a prize of $23,000. So, all you flexible and courageous young folks out there, just imagine drenching those unsuspecting parental figures napping in the sun and getting paid for it too.
